Summary While being towed by the tug SEASPANMONARCH, on a voyage from Texada Island, B.C. to Seattle, WA., the barge SEASPAN240 capsized on 17 July 1996 at 1030.[1] The total cargo of limerock, carried on the deck of the barge, was lost. There were no injuries as a result of the occurrence and no pollution was reported. The overturned barge was subsequently towed to Vancouver, B.C. where it was surveyed and righted. Ce rapport est galement disponible en franais. Other Factual Information Particulars of the Vessels The SEASPAN240 was built in 1962 as a deck-cargo carrying barge of all-welded steel construction, with a designed cargo deadweight of 10,000 long tons (10,160 tonnes). The hull is subdivided by eight transverse and two longitudinal bulkheads forming twenty-one watertight compartments, together with separate fore peak and after peak spaces. The centre compartments were designed as ballast tanks, and are currently arranged as void spaces similar to the wing tanks. A ballast pump room located forward is now redundant and is also arranged as a void compartment. A short forecastle and 3.7m high steel bulwarks, set in from the port and starboard sides of the barge, form a cargo-box on the main deck. The cargo box is fitted with 31 freeing ports at the bottom of each side wall. Every freeing port consists of forty-nine 1-inch (25mm) diameter holes in three rows and two slots at the deck level. The skipper of the tug SEASPANMONARCH was familiar with both the cargo and the route he was planning to follow. The tug departed from Blubber Bay, Texada Island, bound for Seattle, WA., with the barge in tow on 16 July 1996 at 1510. The trip, until the capsizing, was described as normal and the tug and tow followed the recommended traffic pattern route. The length of towline was approximately 500m. At 0700 on 17 July, due to traffic congestion, the skipper decided to leave the southbound lane off Pt. Partridge and cross the traffic separation zone. He would then cross the northbound lane and proceed outside of the traffic scheme closer to the coast north of Admiralty Head on his port side. At about 0800 he rounded Point Partridge at a distance of approximately 1 mile. He steadied the tug and tow on a course 138 True, with the engines driving the propellers at approximately 200 RPM, giving the tug and tow a speed through the water of approximately 7.5 knots. The tide was ebbing and the tug and tow proceeded against the current of approximately 1 knot. Reportedly, in the vicinity of Admiralty Head, eddies caused by the stronger current were observed on the surface. At 1030, the skipper conning the tug saw the barge in tow swinging to approximately 90 to starboard. He immediately placed the throttle control at the 'idle' position to reduce the tug's speed and the pull on the barge. He then released the brake on the drum of the towing winch to slacken the pull even more. However the towline was already sagged low in the water and only a few additional metres came off the drum. In spite of these preventive measures, following the swing the barge started listing to port. In approximately 10 seconds, the barge listed almost 90 and then it overturned quickly. The capsizing took place in a position 4809.0'N, 12241.3'W, approximately 5 cables southwest of Admiralty Head. Subsequently the overturned barge was towed to an anchorage off Port Townsend, U.S.A., where the U.S. authorities conducted an inspection. The barge was then released and towed to Vancouver where a survey was conducted. After a lengthy preparation, it was finally righted on 15 August 1996, using a crane, two tugs and its own ballast tanks. The inspection carried out after the barge was righted revealed that the port side wall of the cargo box was bent inward and badly damaged. All freeing ports were clean and clear, having been completely submerged while the barge was towed in the capsized condition. As an un-manned barge built before 1 September 1977, and not carrying pollutants, the SEASPAN240 is not subject to inspection by the Marine Safety Branch of Transport Canada. The barge is not required to comply with CCG regulatory (Interim) stability requirements. The barge has a Load Line assigned in accordance with the International Convention on Load Lines 1966, with a minimum summer (effective) freeboard of 6' 2[2]. This loadline is directly related to the designed cargo deadweight of 10,000 long tons (10,160 tonnes). However the barge was exempted from provisions respecting load lines by virtue of it being on an international voyage within the treaty zone (Ref. Treaty Series 1934, No. 10, between Canada and the United States, in force July 26, 1934). The treaty and current TC regulations respecting the assignment of international load lines make reference to the boundaries of the treaty zone in which U.S. and Canadian vessels are exempted from these requirements. Measurements recorded prior to and on completion of loading at Blubber Bay Quarry show mean freeboard figures of 21'6 and 4'4 respectively, and a loaded cargo deadweight of 12,717 short tons (11,536 tonnes). The records also indicate that on departure the barge was virtually upright and trimmed approximately 1'0 by the stern. The barge was very heavily laden, so that the mean freeboard recorded on departure was significantly less than the assigned minimum summer effective freeboard of 6'2. Reportedly, the cargo was distributed fairly evenly throughout the cargo-box area, with a maximum height of some 5'6 (1.7m) above the top of the side bulwarks. Conflicting information indicating the configuration of the deck cargo to be comprised of several conical mounds of limestone was also made available. The most likely fore and aft cargo distribution on the SEASPAN240 was derived from and directly related to the recorded departure draughts. Based on the derived cargo distribution, the recorded trim and freeboards, and the cargo deadweight as determined by the loading personnel from the barge's Deadweight Scale, the barge had positive initial transverse stability on departure. However, the range of positive stability was limited because of the low freeboard, and the maximum righting lever was reached at about 8.4 heel. A draught survey carried out by a naval architect after the occurrence to re-verify the barge lightship weight, resulted in a lower figure than that incorporated in the 1985 deadweight scale used by the loading personnel. The lower re-verified lightship resulted from the removal of entrapped material from a previously sealed conveyor compartment within the hull. Consequently the actual total deadweight would have been slightly more than the cargo deadweight recorded on departure. The limerock cargo, consisting of pieces varying in size from a fine dust to approx 75mm, has an angle of repose of approximately 36 to 38. While limestone does not absorb any significant amount of water, its surface can retain rainwater by capillary attraction, making it prone to slipping when its established angle of repose is approached or slightly exceeded. Reportedly, while it was being loaded by a shore conveyor boom, the barge was shifted fore and aft to facilitate the loading. The weather on departure from Blubber Bay and throughout the voyage remained good with light wind and calm seas. However during the night following the departure, the tug and tow encountered rain. Reportedly, at times it was raining heavily. The climatological station of the Environment Canada located on Saturna Island recorded 0.31 (7.9mm) of precipitation on 17 July 1996. According to the tide tables, at the time of the capsizing the predicted tidal current in Admiralty Inlet was ebbing with a rate of approximately 3 knots in the middle of the inlet. The pattern and the rate of the surface current were significantly different near the shore and close to Admiralty Head. The barge SEASPAN240 capsized once before, in 1986. This occurrence is recorded in MCI Report No. 503. It was loaded with 11,296 tons (11,480 tonnes) of limestone rock from Blubber Bay quarry and capsized alongside a discharging wharf at Tilbury Island, B.C. For over 60 years it has been left to the barge owners/operators discretion as to how deep barges can be safely loaded for voyages within the treaty zone of sheltered waters of the west coast of North America.